1. Field of the Invention
This invention relates to an improved control and telemetry signal communication system for satellites, and more particularly to a communications system between a central on-board computer and nodes located throughout the satellite.
2. Description of the Prior Art
In geostationary satellites, a central, on-board command and data handling computer in the satellite communicates with more than 1000 nodes physically located throughout the satellite in order to adequately control and monitor its operation. FIG. 1 is a functional block diagram of a typical prior art satellite telemetry and control system, but showing only six nodes in order to simplify the drawing. Here, each telemetry analog node (here nodes 2 and 5) (e.g. a thermistor monitoring the temperature at a region of the satellite) is connected by a separate pair of wires 12 to provide an analog input to an intermediate control processor 14. Similarly, each digital node 13 (nodes 1, 3, 4 and 6) is connected to the control processor 14 by a separate, dedicated data bus 17. Each data bus may be comprised of a number of parallel wires for parallel data transmission or may comprise a serial data channel for serial data transmission depending upon the node requirements. A redundant digital data bus 19 connects the control processor 14 to a central command and data handling processor 16. The system includes a communications channel 18 for sending and receiving data to and from ground stations while the satellite is in orbit. As will be appreciated by those skilled in the art, the hardware, software, and cabling of the prior art system used to monitor and control the operation of the satellite is expensive, heavy, requires considerable power to operate, and is difficult to integrate into and test as part of the overall satellite system.
An object of this invention is the provision of an analog telemetry and digital command communications system for satellites which provides a uniform interface between the nodes and the central computer and significantly reduces the amount of cabling needed between the nodes and the central computer.